The present invention relates to a power unit which includes a self-oscillating series-resonance converter and which functions to supply a load, such as an electric bulb, a battery charger and/or electronic equipment, wherein the series-resonance converter includes two mutually connected transistors, each of which is intended to be activated by a control transformer, and a series-connected inductor and capacitor, and wherein each transistor and a corresponding series-connected capacitive voltage divider belonging to the transistor and/or a further transistor is connected in parallel with the inductor, capacitor and control transformer, and wherein the load is connected across the capacitor.
A power unit of the aforedescribed kind is known to the art and is found described, for instance, in Swedish Patent Specification No. 7512267-1. This power unit operates in accordance with the series-resonance principle and provides many advantages over other known power units. These advantages include low switch losses at high operating frequencies, while problems relating to radio interference or disturbance are negligible.
One of the drawbacks with a power unit that operates in accordance with the series-resonance principle is that it requires the presence of complicated drive electronics. This results in a high total cost for the manufacture of such a power unit. Since there is a high demand for power units which can be used in low-price equipment, it is desirable to make the drive circuits of the power unit as cheap as possible.